1. Field of the Invention
This invention relates to a knock control apparatus for internal combustion engines, and more particularly to a knock suppression apparatus of ignition timing control type for improving the controllability of internal combustion engines during transient operation.
2. Description of the Prior Art
There are various types of control systems for detecting and suppressing knock phenomena occurring in internal combustion engines, such as fuel control systems, ignition timing control systems and pressure gate control systems. Here the ignition timing control system, which is the most frequently adopted system, will now be explained.
The following describes a knock control (ignition control) apparatus that utilizes the conventional ignition time control system for an internal combustion engine as shown in FIG. 13.
Such an ignition timing control type knock control apparatus is widely known. In the figure, reference numeral 1 designates an acceleration sensor that is attached to the engine to detect the vibration acceleration of the engine. Denoted 2 is a frequency filter that filters the output signal from the acceleration sensor 1 and passes a frequency component of the output signal which is typical of knocking. Designated 3 is an analog gate that eliminates noise from the output signal of the frequency filter 2 which is detrimental to detecting knocking. Reference number 4 indicates a gate timing controller that controls the opening and closing of the analog gate 3 according to the timing of noise occurrence. Denoted 5 is a noise level detector which detects the level of mechanical vibration noise from engine other than knocking. Designated 6 is a comparator that compares the output voltage of the analog gate 3 and the output voltage of the noise level detector 5, and generates a knock detection pulse. An integrator 7 integrates the output pulses from the comparator 6 and generates an integrated voltage according to the intensity of knocking. A phase shifter 8 changes the phase, i.e., the ignition timing of a reference ignition signal according to the output voltage of the integrator 7. A revolution signal generator 9 generates an ignition signal according to a preset ignition advance angle characteristic. A waveform shaper 10 shapes the output of the revolution signal generator 9 and at the same time performs the duty angle control for energization of an ignition coil 12. A switching circuit 11 switches on and off the electric current to the ignition coil 12 according to the output signal from the phase shifter 8, thus producing ignition pulses which are fed to the spark plug (not shown).
FIG. 14 shows the frequency characteristic of the output signal from the acceleration sensor 1. A represents the frequency characteristic when knocking is not present and B represents the frequency characteristic when knocking is present. The output signal of the acceleration sensor 1 contains, in addition to the knock signal (i.e., a signal generated by a knocking phenomenon), mechanical noise of engine and various other noise components such as ignition noise superimposed on the signal transmission paths. Comparison between the frequency curves A and B of FIG. 14 shows that the knock signal has a peculiar frequency distribution characteristic. That is, the presence of knocking is known to produce a clear distinction in the distribution characteristic although there are some variations in the curves depending on the type of internal combustion engine or on the position where the acceleration sensor 1 is mounted. By filtering the frequency components of the knock signal, it is possible to suppress noise of other frequency components than knocking and thereby efficiently detect the knock signal.
FIGS. 15 and 16 show the operation waveforms in each circuit of the conventional apparatus shown in FIG. 13. FIG. 15 represents the mode in which knocking is not present and FIG. 16 represents the mode in which knocking exists. Using FIGS. 15 and 16, we will explain the operation of the conventional apparatus shown in FIG. 13. As the engine runs, the revolution signal generator 9 produces an ignition signal according to the preset ignition timing characteristic. The ignition signal is shaped by the waveform shaper 10 into a pulse with a desired duty angle, which drives the switching circuit 11 through the phase shifter 8. The switching circuit 11 switches on and off the electric current to the ignition coil 12. When the electric current to the ignition coil 12 is interrupted, the coil induces an ignition voltage, which in turn fires the spark plug, initiating the combustion of air-fuel mixture in the engine cylinder. All engine vibrations that occur during operation of the engine are detected by the acceleration sensor 1.
When there is no knocking, engine vibrations due to knocking are not generated. But as there are always other mechanical vibrations, the output signal of the acceleration sensor 1 contains mechanical noise as well as ignition noise that is carried on the signal transmission path at time of ignition F, as shown in FIG. 15A.
The mechanical noise is substantially suppressed when the sensor signal is passed through the frequency filter 2, as shown in FIG. 15B. The ignition noise component, however, is large in magnitude compared with the mechanical noise component and thus may be output at high level after the sensor signal has passed through the frequency filter 2. With such an output waveform, the ignition noise may be mistaken for a knock signal. To prevent this, the analog gate 3 is closed at the instant of ignition for a predetermined period by the output of the gate timing controller 4 (FIG. 15C) which is triggered by the output of the phase shifter 8, in order to block the ignition noise which would otherwise be output from the frequency filter 2 to the comparator 6. Then, in the output of the analog gate 3 there remains only a low level of mechanical noise, represented by a of FIG. 15D.
The noise level detector 5 responds to changes in the peak value of the output signal from the analog gate 3 and generates a dc voltage slightly higher than peak value of the mechanical noise (b of FIG. 15D). The noise level detector 5 has a characteristic of being able to respond to relatively slow changes in the peak value of ordinary mechanical noise. Since, as shown in FIG. 15D, the output b of the noise level detector 5 is larger than the average peak value of the output signal a of the analog gate 3, the comparator 6 which compares these signals produces nothing as shown in FIG. 15E. Thus, noise signals other than the knocking signal are all eliminated.
The output voltage of the integrator 7 therefore remains zero as shown in FIG. 15F and the phase angle of the phase shifter 8 is also zero. The phase angle means the phase difference between the output of the wave shaper 10 (FIG. 15G) and the output of the phase shifter 8 (FIG. 15H). In other words, the open/close phase of the switching circuit 11 which is driven by the phase shifter output (FIG. 15H), i.e., the current interrupting phase of the ignition coil 12, is in phase with the reference ignition signal of the wave shaper output (FIG. 15G). The ignition timing is therefore equal to the reference ignition timing.
Next, when knocking occurs, the output of the acceleration sensor 1 contains a noise signal caused by knocking at a time a certain duration after the ignition timing, as shown in FIG. 16A. The signal that has passed through the frequency filter 2 and the analog gate 3 will have a large knock signal superimposed on the mechanical noise, as shown at c of FIG. 16D.
The leading edge of the knock signal that has passed through the analog gate 3 is very steep, so that the level change in the output voltage d of the noise level detector 5 (substantially equal to the voltage b of FIG. 15D) lags with respect to the knock signal. As a result, the inputs to the comparator 6 will be those represented by c and d of FIG. 16D and the comparator 6 produces its output pulses as shown in FIG. 16E.
The integrator 7 integrates the pulses entered and then generates an integrated voltage as shown in FIG. 16F. The phase shifter 8 retards the output signal of the waveform shaper 10 (FIG. 16G, i.e., reference ignition signal) according to the output voltage of the integrator 7, so that the output of the phase shifter 8 lags behind the reference ignition signal of the waveform shaper 10 and activates the switching circuit 11 at a phase shown in FIG. 16H. As a result, the ignition timing is retarded, suppressing knocking. In this way, the processing shown in FIGS. 15 and 16 is repeated to perform the optimum ignition timing control.
The conventional apparatus of FIG. 13 is constructed as described above. The rate of reduction in the output of the integrator 7, i.e., the speed at which the ignition timing is returned and advanced toward the reference, is represented by a large time constant, of the order of several seconds, per one degree of engine rotation. Thus, properly regulating the reduction rate is particularly important in preventing large knocking, which would occur when the ignition timing is returned toward the advance side at too high a speed, rapidly entering the knock region.
To optimumly control the speed of advancing the ignition timing by regulating the rate of reducing the integrator output, it is necessary to determine the accurate intensity of each knocking detected. To determine the knock intensity or magnitude from the output of the integrator 7 requires determining the integrator outputs immediately before and after the knock detection and calculating the difference between them, i.e., a change in the integrator output at each knock detection. This process requires complex calculation. The knock magnitude cannot be obtained by simply reading the value of the integrator 7 when knocking is detected. For example, the output of the integrator 7 before the knock occurs has to be stored in memory and, when knocking occurs, it is necessary to calculate the difference between the integrator outputs immediately before and after the knocking.
The engine control in recent years has become increasingly sophisticated and there is a trend toward employing a design in which precision control is performed for individual cylinders to keep the entire cylinders in an optimum state of combustion and thereby enhance engine output. To perform such a sophisticated control, it is necessary to detect the magnitude of each knocking as it occurs and also determine the magnitude of knock for each cylinder. However, to determine the magnitude of each knock from the output of the integrator 7 in the conventional apparatus requires complex calculation as mentioned above. And determining the magnitude of knock for each cylinder results in an increased size of the circuit. These are the problems with the conventional apparatus.
To solve these problems, a knock control apparatus was proposed which can easily detect the magnitude of each knocking as well as the magnitude of knock for each cylinder, and thereby make the knock control easy.
By referring to FIGS. 17 through 22, we will describe another conventional apparatus which realizes the above proposal. In FIG. 17, components 1 to 6 and 11 and 12 are identical with those of FIG. 13 with the same reference numbers and thus their description will be omitted. Denoted 21 is a cylinder pulse generator that generates a cylinder pulse corresponding to the ignition action of each cylinder in the engine. Designated 22 is a duty ratio control circuit that receives the cylinder pulse and generates a duty ratio-controlled ignition pulse to secure the sufficient energization time for the ignition coil 12. A phase shifter 23 performs the control of retarding the ignition pulse by an angle corresponding to the control voltage. An integrator 24 receives the knock pulse from the comparator 6 and outputs an integrated voltage proportional to the duration of the knock pulse. This integrator 24 is different from the integrator 7 used in the preceding conventional apparatus of FIG. 13 in that it maintains its output up to the ignition timing and resets the integrated voltage at each ignition according to the ignition pulse output from the phase shifter 23, rather than gradually reducing the integrated voltage with the elapse of time. Designated 25 is an A/D converter which converts the integrated voltage from the integrator 24 into a digital signal. 26 designates a distributor circuit which distributes the digital signal to the cylinder where knocking occurred. This embodiment represents a four-cylinder engine and the distributor circuit 26 in this embodiment therefore produces four outputs, equal in numbers to the cylinders. Denoted 27 to 30 are memories each of which corresponds to one of the four cylinders and stores digital signal from the distributor circuit 26. For instance, memory 27 stores the amount of knock that occurs in the first cylinder. A clock generator 31 produces pulses at predetermined intervals and supplies pulses to the memories 27-30 to perform subtraction on the values stored in them. A selector circuit 32 selects only the data from the memories 27-30 that relates to the fired cylinder. A reference pulse generator 33 generates a reference pulse for the reference cylinder--one of the four cylinders. Denoted 34 is a cylinder selection pulse generator circuit, which receives the reference pulse and the ignition pulse from the duty ratio control circuit 22 and generates cylinder selection pulses one after another to make the operation condition of the distributor circuit 26 and the selection circuit 32 to conform to the specified cylinder. A failure detection circuit 40 detects failures such as a broken signal wire between the acceleration sensor 1 and the frequency filter 2 or a ground fault. It also detects abnormal voltages at the output of the noise level detector 5 and enters a fail signal into the integrator 24. At the same time the failure detection circuit 40 sends fail signals KF to other fuel control apparatus and vehicle diagnostic apparatus.
FIGS. 18 and 19 show the operation waveforms of circuits shown in FIG. 17. The waveforms in these figures are identical with those of FIGS. 15 and 16 that represent the conventional apparatus if they are assigned like reference numerals.
The fundamental operation will be explained by referring to FIGS. 18 and 19. When the engine is not producing knocking, the two inputs to the comparator 6 will be as shown in FIG. 18D. Since there is no knock signal at e in FIG. 18D, no pulse will be produced at the output of the comparator 6 as shown in FIG. 18E. Thus, no pulse is produced at the output of the integrator 24 (FIG. 18F). Therefore, memories 27-30 contain no values and the selection circuit 32 has no output, so that there is no phase difference between the input (FIG. 18G) and the output (FIG. 18H) of the phase shifter 23, leaving the ignition timing at the reference position.
Next, the operation performed when knocking occurs in the engine will be described by referring to FIG. 19. The two inputs to the comparator 6 will be as shown in FIG. 19D and since a knock signal appears at g in FIG. 19D, the comparator 6 produces a knock pulse as shown in FIG. 19E. The knock pulse is integrated by the integrator 24. To perform knock detection for each cylinder, the output of the integrator 24 is reset by the output of the phase shifter 23 each time the cylinders are ignited. For this reason, during the time from the knock detection to the resetting, the output of the integrator 24 is kept at a constant value. These operations are performed at each ignition interval. This is where this conventional embodiment differs from the preceding conventional apparatus of FIG. 13. The output of the integrator 24 (integrated voltage) is converted into digital signals by the A/D converter 25. The distributor circuit 26 identifies the cylinder where knocking occurred, according to the cylinder selection pulse from the cylinder selection pulse generator 34. When, for example, the cylinder where knocking occurred is the third cylinder, the distributor circuit 26 then inputs the digitized integrated voltage from the A/D converter 25 into memory 29 associated with that cylinder. The memory 29 then stores the integrated voltage fed from the distributor circuit 26. According to the cylinder selection pulse from the cylinder selection pulse generator 34, the selection circuit 32 selects the memory 29 that corresponds to the third cylinder, and transfers the output of the memory to the phase shifter 23. Here we are dealing with the case where knocking occurred in the third cylinder, so when the third cylinder is fired, the output of memory 29 is chosen and entered into the phase shifter 23. In FIG. 19, knocking also occurred in the next cylinder, so that in an ordinary 4-cylinder engine, knocking is determined to have occurred in the fourth cylinder. In this case, the output of the integrator 24 is picked up by the distributor circuit 26 which stores it in memory 30. Then the selection circuit 32 selects the memory 30 and transfers its output to the phase shifter 23 when the fourth cylinder is ignited.
Now, the control for individual cylinders will be described in detail by referring to waveforms in FIG. 20. In the figure, (s) represents the ignited cylinder number; (e) the output of the comparator 6; (f) the output of the comparator 24; (j), (k), (l) and (m) the stored values in memories 27-30; (p) the output of the selection circuit 32; and (g) and (h) the input and output of the phase shifter.
As shown in FIG. 20(e), there are knock pulses at the output of the comparator and knocking occurs in the order of third, second, third, fourth and second cylinder. These knock pulses are converted by the integrator 24 into the integrated voltage, which is output as shown in FIG. 20(f). K1, K2, K3, and K5 represent the levels of knocking detected, with the magnitude gradually increasing up to K5, which is the largest. At time t1, knocking occurs in the third cylinder and the output of the integrator 24 reaches the voltage K5. The voltage K5 is converted by the A/D converter 25 into a digital signal, which is then entered into the distributor circuit 26. The distributor circuit 26 selectively outputs the digitized integrated voltage K5 to the memory 29 at the ignition timing t2 of the fourth cylinder. As a result, the digitized integrated voltage K5 is memorized in the memory 29 at time t2, so that the value contained in the memory 29 becomes the voltage K5 (FIG. 20(l)). Next, at time t3, knocking occurs in the second cylinder and the knock pulse is integrated by the integrator 24 into the integrated voltage K5, which is converted into a digital signal by the A/D converter 25. The digitized integrated voltage K5 is selectively input to the memory 28 by the distributor circuit 26 and, at time t4, is stored in the memory 28 (FIG. 20(k)). Time t4 is an ignition timing for the first cylinder and from this point onward the third cylinder enters the ignition control sequence. At this time since the voltage K5 is already stored in memory 29, the selection circuit 32 outputs the voltage K5 (FIG. 20(p)) to the phase shifter 23. Then the phase shifter 23 retards the next ignition timing by an angle .theta.5 corresponding to the voltage K5, the angle .theta.5 being equal to a phase delay of the output of the phase shifter 23 (FIG. 20(h)) relative to its input (FIG. 20(g)). As a result the next ignition occurs at time t5. Although the ignition is retarded from the reference ignition timing by .theta.5 and performed at time t5, knocking occurs again at time t6 in the third cylinder. This knocking has the level of K2 and the corresponding integrated voltage K2 is entered into memory 29 at the next ignition timing (time t7) of the fourth cylinder. At this time the memory 29 already contains the voltage K5, so that the voltage K2 is added to the voltage K5 and a new voltage K7 is memorized instead (FIG. 20 (l)). For the ignition at time t7 (reference ignition timing), knocking occurs at time t8 in the fourth cylinder and the integrated voltage K3 is output. The voltage K3 is stored in memory 30 at the next ignition timing (time t9) of the second cylinder.
From time t7 the next ignition control sequence for the second cylinder is started. At this time, the voltage K5 is already stored in memory 28 and the selection circuit 32 selectively inputs the voltage K5 to the phase shifter 23. As a result, the next ignition timing will be t9, which is .theta.5 retarded from the reference, .theta.5 corresponding to the voltage K5. For the ignition at time t9, knocking occurs at time t10 in the second cylinder, causing the integrated voltage K1 to be output. The voltage K1 is added to memory 28 at time t11 of the next ignition timing, with the result that the contents of the memory 28 will be voltage K6. From time t11 the ignition control sequence for the third cylinder starts. At this time, the memory 29 contains the voltage K7, so that the next ignition timing t12 will be .theta.7 retarded from the reference. In this way, the similar ignition point retarding control is repeated and the next ignition timing (t13) for the fourth cylinder will be 83 retarded from the reference. And the next ignition timing (t14) for the second cylinder will be lagging by .theta.6 from the reference.
As described above, the ignition timing is retarded in accordance with the magnitude of knocking detected (integrated voltage). When knocking no longer occurs in the engine, the ignition timing must be advanced toward the reference at the specified rate to come close to the knock limit. In this embodiment, the values stored in the memories 27-30 are subtracted by the clock of the clock generator 31 at the specified rate to make the stored values smaller, reducing the voltage to be input to the phase shifter 23 and therefore the retarding angle, so that the ignition timing will come close to the reference.
If the components in this embodiment--such as the phase shifter 23, a group of components from the integrator 24 to selection circuit 32, and the cylinder selection pulse generator circuit 34--are constructed using computer, it is possible to develop a sophisticated control system that permits precision control including engine fuel control.
Furthermore, as with the conventional apparatus of FIG. 13, it is possible to retard the ignition timings for all cylinders by the same angles. In this case, the distribution circuit 26 and the selection circuit 32 for selecting the cylinder are fixed, and only one of the four memories 27-30 need be used. It is also possible to switch between the individual cylinder control and the all-cylinder control depending on circumstances.
The failure detection circuit 40 outputs a fail signal KF when a signal wire connecting the acceleration sensor 1 and the frequency filter 2 is broken, when a ground fault occurs or when the output of the acceleration sensor 1 is not normally entered into the frequency filter. Of these failures, in general, break of the signal wire is most likely to occur (for example, poor contact in the connector). The failure detection circuit 40 also produces a fail signal KF when the operating condition of the noise level detector 5 becomes abnormal. In other words, this circuit 40 detects when the operation deviates from the normal setting range even though the signal wire between the acceleration sensor 1 and the frequency filter 2 is normal. For example, the signal to be processed may become very large making it impossible to output the normal comparison reference voltage. The integrator 24, when it receives the fail signal KF from the failure detection circuit 40, is activated irrespective of the signal from the comparator and outputs the integrated voltage at time of failure. FIGS. 21 and 22 show one example of integrated voltage in the event of failure. In the case of FIG. 21, the integrator 24 always outputs the maximum possible integrated voltage VoMAX. The maximum integrated voltage VoMAX is repetitively reset at the ignition timing (at time F) by the ignition signal output from the phase shifter 23 so that it will become zero each time ignition occurs. In the case of FIG. 22, the integrator 24 is not reset by the ignition signal from the phase shifter 23. This is accomplished by nullifying the ignition signal fed to the integrator 24 by the fail signal KF from the failure detection circuit 40. Since the integrated voltage VoMAX is output at all times, it is stored in all memories 27-30. Thus the ignition timing is automatically set to the desired time which will not produce knocking when some failure occurs. In this example, the ignition timing is controlled by using the maximum value VoMAX of the output of the integrator 24 in the event of failure. It is noted that the control variable may be other than the maximum value and may be an intermediate value. It is also possible to include in this control variable the engine knock characteristic and other characteristics. The fail signal KF may be supplied to a fuel control apparatus to achieve the overall control of an engine. Or it may be entered into a diagnostic apparatus to set off an alarm. It is also possible to include other control equipment to develop a more comprehensive control system.
The conventional knock suppression apparatus is constructed as described above and thus can control the knock value below a desired level (normally smaller than a so-called trace knock). However, during the transient operating condition, as when the engine is accelerating, there are varying operating conditions among various parts of the engine due to their differing transient characteristics. For this reason, knocking occurs more frequently than during the steady state operating condition. Therefore, the control characteristic which suppresses knocking during the steady state operation down to trace knock is not sufficient for the knocking that occurs during transient condition. In other words, the controllability during transient condition is not good. That is, the conventional apparatus has the drawback that the knocking during transient operating condition is greater in magnitude and trace knocks occur more frequently than during the steady state condition, causing unpleasant noise.
In the above-mentioned conventional knock control apparatus, the integrator 24 is reset by the ignition signal output from the phase shifter 23 so that the integrated voltage--an output of the integrator 24--becomes zero at each ignition timing. When this resetting, necessary to read the magnitude of knocking at each ignition (each time knocking occurs), is repeated for every ignition as in the conventional apparatus of FIG. 17, the detection of knock itself may be affected and in the worst case cannot be done at all depending on the setting value of the reset time.
In other words, in the system where the reset time is set with a constant-time pulse, which is easily dealt with, the above-mentioned problem arises when the engine runs in the high revolution speed zone in which the ignition cycle is short. That is, if the reset time is constant, the reset time--which is converted into the rotating angle of the engine--becomes relatively large as the revolution speed of the engine increases and the reset time may encompass the area where knocking occurs after ignition. In high rotating speed regions where the cycle is short, the reset time thus set may cover the knocking region.
If the reset time is set with a constant angle, whose processing is complex, the reset time will not encompass the knocking region regardless of the revolution speed of the engine. However, the reset time (absolute time) becomes short in the high revolution region, which gives rise to the possibility that the integrated voltage in the integrator 24 cannot reliably be reset to zero.
Therefore, a primary object of the invention is to provide a knock control apparatus which can suppress knocking that occurs during transient operating condition of the engine down to a suppression level equal to the one during the steady state operation and which can prevent knocking over a long period of time.
A second object of the invention is to provide an ignition timing control apparatus for internal combustion engines which makes use of the knock occurring mechanism (i.e., during the normal operating condition of the engine the interval of knocking is, on average, of the order of several seconds and knocks occur a specified number of ignition periods apart); which sets the reset period longer than the ignition cycle; and which permits resetting that is virtually the same as the above-mentioned reset processing.
A means to achieve the first objective makes the control quantity for suppressing the knock detected larger during the transient operating condition than during the steady state operation so as to suppress knocking during the transient operation below a level of trace knock thus improving the transient operation responsiveness of the system.
A means to achieve the second objective provides a reset generation circuit to generate a reset pulse that resets the integrated voltage of the integrator to zero in synchronism with the ignition signal at intervals of more than double the ignition cycle.